The invention relates to “active implantable medical devices” as defined by the Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, and particularly implantable devices that continuously monitor the heart rate and if necessary deliver to the heart electrical stimulation, resynchronization and/or defibrillation pulses in case of arrhythmia detected by these devices.
The invention relates especially, but is not limited to, those devices that are in the form of an autonomous capsule intended to be implanted in a heart chamber, including the ventricle.
These capsules are free of any mechanical connection to an implantable (such as a housing of the stimulation pulse generator) or non-implantable (external device such as programmer or monitoring device for patient remote monitoring) main device, and for this reason are called “leadless capsules” to distinguish them from electrodes or sensors disposed at the distal end of a conventional probe (lead), which is traversed throughout its length by one or more conductors galvanically connecting the electrode or sensor to a generator connected to an opposite, proximal end of the lead.
Note, however, that the autonomous nature of the capsule is not inherently a necessary feature of the invention.
The implantation of a leadless capsule in the right or left ventricle allows very simple “single chamber” (stimulation of a single, ventricular, cavity) configuration of a pacemaker. The leadless capsule is provided with a detection/stimulation electrode in contact with the wall of the ventricle, which enables it to detect the presence or absence of a spontaneous ventricular depolarization wave, as well as the occurrence time of this wave (ventricular marker) and, if necessary, to deliver a stimulation pulse in case of missing or late spontaneous depolarization, so as to cause contraction of the ventricle.
However, this mode of operation is limited to a single ventricular chamber stimulation, that is to say in which an escape interval (IE) is programmed to cause stimulation if the time since the last detection or stimulation of the ventricle exceeds the length of this interval, or do nothing in case of detected spontaneous ventricular depolarization.
This mode of operation has the disadvantage that ventricular pacing is not synchronized with the emptying of the atrium, and the pacing rate will not adapt to the sinus rhythm at a given time (sinoatrial rhythm). This can be annoying in case of physical activity because the pace will not accelerate despite increased physiological needs. For adaptation to the rhythm of the patient, there are solutions implementing rate-response servo methods, but they are sub-optimal compared to methods based on the detection of atrial activity, as long as the patient is not chronotropic incompetent.
In the absence of sinus node dysfunction, a VDD mode may be preferred to a single ventricular chamber mode. This VDD mode is obtained by programming a traditional dual chamber pacemaker, but may also be obtained with a single lead device having two atrial “floating” electrodes for atrial detection, and bipolar ventricular stimulation/detection electrodes. However, any atrial pacing is impossible. The detection of atrial activity, that is to say the moment at which the atrium contracts, allows determining the patient's instant sinus rhythm (from successive RR intervals) and thus calculating and applying an atrioventricular delay (AVD) based on that rhythm. Then the pacemaker will operate in VDD mode (ventricular pacing from the signals collected on both the ventricle and atrium).
This method is not possible with a leadless capsule, which by definition has no lead and thus contains no element located in the atrium area.
In such cases, it would be beneficial to detect atrial activity from the leadless capsule implanted in the right or left ventricle, without any opportunity to collect a signal reflecting the electrical activity of the atrium.
The same issue may arise in certain situations with a conventional pacemaker (a device including an endocardial lead connected to a remote generator), for example in case of rupture of an atrial lead, or when the signals delivered using a floating electrode (“floating dipole” configuration) are not of sufficient quality to be able to derive a sufficiently reliable atrial activity signal.
Various proposals have been made to solve the problem of collection of an atrial signal by an endocardial leadless capsule implanted in the right or left ventricle.
US 2013/0325081 A1 describes a leadless capsule in which one of the ends is anchored to the right ventricle and whose opposite free end is provided with an extension having a wire or antenna shape extending into the right atrium. This extension is in contact with the wall of the right atrium and allows the detection/stimulation in the cavity, enabling an operation of the capsule in the DDD or DDDR modes. In another embodiment, the capsule contains no extension, but is provided, at its free end opposite to the anchor point, electrodes for enabling far-field detection of the electrical activity of the right atrium, with application of specific filters or morphological recognition of electrical signals collected at the capsule by these electrodes.
Comparably, US 2013/0138006 A1 uses electrodes on areas of the capsule which are not in contact with the wall of the ventricle, in order to collect far-field electrogram signals. The detection of atrial activity is based on a comparison between the near-field and the far-field, the atrial activity being detected when the far-field signal exceeds a threshold and the near-field signal does not exceed it. This dual atrial/ventricle detection from ventricular electrodes, only based on electrical far-field/near-field signals, remains complex to implement and, in practice, is insufficiently reliable to detect the presence or absence of atrial activity with a high degree of certainty.
EP 2471447 A1 describes a configuration in which a left ventricular stimulation produced by an epicardial capsule is synchronized on a left atrial pacing, also produced by an epicardial capsule. The synchronization is performed by analysis of signals conducted by the heart tissue, the ventricular capsule operating as the slave of the atrial capsule. However, this device involves the presence of an atrial capsule and implanting epicardial capsules in contact with the outer wall of the myocardium, which is a much more complicated procedure than the implantation of a single endocardial capsule.
Yet another proposal is that of US 2013/0123872 A1, wherein a single leadless capsule is used, but placed in the atrium. The problem then is to detect ventricular activity from the atrium, which implies the implementation of complex filters to prevent interference (cross-talk) between atrial and ventricular signals.
None of these devices described above provide a satisfactory solution to the issues described above, because all are based on the collection of electrical information reflecting the activity of the atrium and requiring an atrial electrode.
Pacemakers using a lead with an EA sensor are known, as described for example in EP 2189180 A1 (Sorin CRM S.A.S.). This proposes to adjust the AVD taking as the starting point of the delay the end time of the EA4 wave. The search for EA4 component is performed after detection of a P wave (spontaneous atrial depolarization wave) or after an atrial stimulation A. This configuration requires the availability of a marker of atrial electrical activity (P/A) and it is therefore not applicable to the case of a leadless capsule devoid of collection methods of the electrical activity of the atrium.
Other stimulators using a lead with an EA sensor are described in EP 2499971 A1 (Sorin CRM), which involves an analysis technique of the EA signal to dynamically adjust therapy according to the status of the patient, and in EP 2311524 A1 (Sorin CRM), which involves the concomitant optimization of AVD and VVD based on the results of the analysis of the EA signal.
But neither of these documents relates to the specific problem described above, namely the detection of atrial activity by a device (such as a leadless capsule) implanted in the right or left ventricle, but without an atrial lead or other methods or opportunity to collect a signal reflecting the electrical activity of the atria.
EP 2189182 A1 (Sorin CRM S.A.S) proposes the detection of atrial activity from the EA4 component to confirm atrial capture after stimulation. Detecting the EA4 component is based on energy analysis in sliding windows which validate the presence of a contraction if the energy exceeds a given threshold. For each cardiac cycle, the search window of EA4 component is referenced to the atrial stimulation or detection instant, presupposing as in the previous case the knowledge of a marker of atrial electrical activity (P/A). In any event, to the extent that it is to confirm or not the capture after stimulation of the atrium, the device is necessarily provided with an atrial electrode, the purpose of which is precisely to allow this stimulation of atrium.
None of these documents therefore disclose a method to detect atrial activity without having first a marker of electrical activity to recognize and confirm the existence of atrial contraction.
EP 2092885 A1 (Sorin CRM S.A.S.) describes a processing method of extracting the principal components of an EA signal. This document substantially discloses methods of extracting EA1 and EA2 components corresponding to the two main heart sounds, these methods being possibly transposed to the detection of the EA4 component. The detection of the EA1 and EA2 components requires the definition of predefined search windows based on ventricular electrical markers and depending on the heart rate. However, this does not disclose any method that would define these windows to possibly detect the EA4 component without a marker of atrial electrical activity.